Lower ISO for sharpest image

Use a low ISO as possible. When you take pictures using a tripod with a low-light situations, do not increase ISO value. Try to stick with a low ISO (ISO 200, 100 or 50) to obtain the sharpest images and clean.

But if you do not use a tripod, there is no alternative but to raise the ISO.

TIPS: Set the camera on Shutter Priority and choose a speed that matches or exceeds your lens focal length (eg, 180mm means you'll be shooting at a speed of 1/200 sec)